Vulnerable plaques are lipid filled cavities that form within the wall of a blood vessel. These plaques, when ruptured, can cause massive clotting in the vessel. The resultant clot can interfere with blood flow to the brain, resulting in a stroke, or with blood flow to the coronary vessels, resulting in a heart attack.
To locate vulnerable plaques, one inserts a catheter through the lumen of the vessel. The catheter includes a delivery fiber for illuminating a spot on the vessel wall and one or more collection fibers for collecting scattered light from corresponding collection spots on the vessel wall. The delivery fiber, and each of the collection fibers form distinct optical channels within the catheter. The catheter used for locating plaques is thus a multi-channel catheter.
In operation, a light source outside the catheter introduces light into the delivery fiber. A detector, also outside the catheter, detects light in the collection fiber and generates an electrical signal representative of that light. This signal is then digitized and provided to a processor for analysis.
A vulnerable plaque can be anywhere within the wall of the artery. As a result, it is desirable to circumferentially scan the illuminated spot and the collection spot around the vessel wall. One way to do this is to spin the multi-channel catheter about its axis. However, since neither the light source nor the processor spin with the catheter, it becomes more difficult to couple light into and out of the delivery and collection fibers while the catheter is spinning.